Low-noise process for pavement fragmentation

ABSTRACT

A low noise method of fragmenting pavement wherein a continuous free surface delineating the area within which the pavement is to be fragmented is created. Thereafter, the pavement within this delineated area is pre-weakened by fracturing it. While the continuous free surface and the pre-weakening of the pavement within this delineated area can be accomplished in numerous different ways, it is preferred to use microwave energy to fracture and pre-weaken the pavement. After having pre-weakened the pavement, the pavement is impacted with a series of water slugs or jets which pressurize all or part of the fracture network displacing or unkeying the pavement fragments bounded by these fractures so as to facilitate their removal. The displaced pavement fragments then can be removed by conventional means, such as shoveling. By pre-weakening the pavement in the abovedescribed fashion, and then pressurizing all or part of the fracture network with a series of water slugs or jets, the energy required is far less and the breakage rate is far greater.

lJnited States Patent 1 Anderson et al.

[ Dec. 111, H973 LOW-NOISE PROCESS FOR PAVEMENT FRAGMENTATION [75] Inventors: Philip J. Anderson, Deerfield, 111.;

James W. Dally, College Park, Md.

[73] Assignee: The Institute of Gas Technology, Chicago, Ill.

[22] Filed: May 17, 1972 [21] Appl. No.: 254,156

[52] U.S. Cl. 299/14, 299/17 [51] Int. Cl. Elllc 23/09 [58] Field of Search 299/14, 17; 175/11-16 [56] References Cited UNITED STATES PATENTS 3,614,163 10/1971 Anderson 299/14 3,704,914 12/1972 Fletcher 299/14 Primary Examiner-Ernest R. Purser Attorney-Jack E, Dominik et a1.

[57] ABSTRACT A low noise method of fragmenting pavement wherein a continuous free surface delineating the area within which the pavement is to be fragmented is created. Thereafter, the pavement within this delineated area is pre-weakened by fracturing it. While the continuous free surface and the pre-weakening of the pavement within this delineated area can be accomplished in numerous different ways, it is preferred to use microwave energy to fracture and pre-weaken the pavement. After having pre-weakened the pavement, the pavement is impacted with a series of water slugs or jets which pressurize all or part of the fracture network displacing or unkeying the pavement fragments bounded by these fractures so as to facilitate their removal. The displaced pavement fragments then can be removed by conventional means, such as shoveling. By pre-weakening the pavement in the above-described fashion, and then pressutizing all or part of the fracture network with a series of water slugs or jets, the energy required is far less and the breakage rate is far greater.

4 Claims, No Drawings LOW-NOISE PROCESS FOR PAVEMENT FRAGMENTATION This invention relates to an efficient, low noise method of fragmenting pavement of concrete or other similar mate rials, within a pre-defined area, to facilitate its removal. The term pavement as used herein is intended to include roads, streets, sidewalks and other slab-type surfaces of concrete or other similar materials, with or without reinforcing rods or mesh therein.

The apparatus presently most commonly used for breaking solid material such as those mentioned above is the pneumatic hammer. While extremely effective, the use of pneumatic hammers often causes public complaints when they are used in densely populated areas. The reason is that both the pneumatic hammer itself and the air compressor that supplies high pressure air to the hammer produce irritating noise of high intensity. This noise is particularly objectionable in areas where hospitals and schools are located. This noise also excludes, or at least restricts, the scheduling of excavation operations at night which, in many cases, such as pavement removal for repairing or laying underground cables and/or pipes, would reduce the down time and the inconvenience to the public.

Accordingly, recently, considerable effort has been and is being made to develop a low noise method for breaking solid materials, particularly pavement. Electric and gas utility companies are especially interested in the development of such a method because of the need to remove pavement to lay new underground cables and pipes, or to repair existing cables and pipes.

In U.S. Pat. No. 3,614,163, issued Oct. 19, 1971, there is disclosed a low noise method for breaking solid material such as pavement which generally includes the steps of creating a continuous or discontinuous free boundary surface about and defining the area of the surface to be broken or fragmented. After creating this free boundary surface, the method contemplates imparting to this defined area high intensity, short duration compressive wave pulses of such number, location and intensity that these compressive waves when reflected at the free surface as tensile wave pulses will exceed the tensile strength of the pavement and cause the latter to break up so as to produce fragments of a desired size for subsequent removal. In accordance with the disclosure of this patent, these high intensity, short duration compressive wave pulses can be imparted to the pavement by means of a water jet or cannon.

While this method of fragmenting the pavement is extremely effective, the power requirements for producing the high pressure jets of water -to establish these compressive wave pulses in the pavement is quite high, and the required pressure is in the neighborhood of 80,000 to 100,000 psi.

1n U.S. Pat. No. 3,601,448, issued Aug. 24, 1971, there is disclosed another low noise method for breaking solid material which involves coupling microwave energy into the solid material such as concrete or rock to thermally induce stresses leading to failure in compression or tension, in a known and predictable manner. The apparatus for coupling the microwave energy into the solid material is adapted to generate independent heating patterns by using, for example, at least two or more microwave applicator horns that are spaced apart from each other. The applicator horn or horns for generating the heat patterns are positioned on or slightly above the solid material to be fractured. The spaced heat patterns or zones produced cause the heated material to grow or expand, due to its coefficient of heat expansion, so as to place high tensile forces or stresses on the unheated material between the heat patterns. These forces or stresses cause failure to occur between the heat patterns, and ultimately across the heat patterns themselves. In this manner, a substantially straight crack along a desired course between adjacent heat patterns can be produced. The crack that is generated is a crack which extends through the solid material.

The method and apparatus of this latter patent can be used in the process disclosed in the above-discussed U.S. Pat. No. 3,614,163, to create the continuous or discontinuous free boundary surface about and defining the area of the surface to be broken or fragmented. One difficulty encountered in fragmenting the pavement using the microwave energy is that the cracks formed in the pavement are not vertical, as would be formed, for example, with a saw cut, but are rather jagged cracks. As a result, the area of pavement to remove is still keyed with the adjacent pavement so that, in most cases, this area to be removed must subsequently be fragemented. The method therefore is not particularly effective or practical for use in fragmenting the pavement, and thus other means are normally employed. These means are conventional means such as the irritating, noise-producing pneumatic hammer. The advantages gained by the use of the accompanying low noise method and apparatus are lost. 7

Having developed these two previous methods of fragmenting solid material such as pavement and realizing the shortcomings of both of these prior methods, it has now been found that the two methods can be combined and slightly modified to produce a new method which is far superior to either of these prior methods in its effectiveness in fragmenting pavement in a fashion such as to permit the pavement to be readily removed. This new method can be generally described with the following sequence of operations. In this case, as in U.S. Pat. No. 3,614,163, a continuous free surface delineating the area within which the pavement is to be fragmented is created. Thereafter, the pavement within this delineated area is pre-weakened by fracturing it. While the continuous free surface and the preweakening of the pavement within this delineated area can be accomplished in numerous different ways, it is preferred to use the low noise method and apparatus disclosed in U.S. Pat. No. 3,601,448. In other words, it is preferred to use microwave energy to fracture and preweaken the pavement. After having pre-weakened the pavement, the pavement is impacted with a series of water slugs or jets which pressurize all or part of the fracture network displacing or unkeying the pavement fragments bounded by these fractures so as to facilitate their removal. The displaced pavement fragments then can be removed by conventional means, such as shoveling. By pre-weakening the pavement in the abovedescribed fashion, and then pressurizing all or part of the fracture network with a series of water slugs or jets, the energy required is far less and the breakage rate is far greater.

Accordingly, it is an object of the present invention to provide improved low noise method of pavement removal.

More particularly, it is an object to provide an improved low noise method of fragmenting pavement, within a defined area, to facilitate its removal.

Still another object is to provide an improved low noise method which generally is far more efflcient in operation than most low efficiency, high noise methods presently used to fragment such type surfaces.

A still further object is to provide an efficient, low noise method of fragmenting such type surfaces which is of such a low noise level that operations can be conducted at night, with little, if any, objection from the public.

A still further object is to provide a low noise method of fragmenting pavement which permits the latter to be more readily removed after being fragmented.

More particularly, as indicated above, the first step in the sequence of operations for pavement fragmentation in accordance with the present invention is to create a continuous free surface, in the form of a fracture or cut which provides a perimeter separation, delineating the pavement which is to be fragmented.

This step can be performed in a number of different ways, including but not limited to sawing, using an electron beam, a laser, a force flame or plazma torch, or by jet piercing, erosion cutting or abrasion cutting the pavement. As indicated above, however, the continuous free surface preferably is formed using microwave energy. For this purpose, a microwave applicator of the type disclosed in the above-mentioned US. Pat. No. 3,601,448 can be used, to direct microwave energy against the pavement through applicator horns which are positioned in a fashion such as to generate a substantially straight crack in the pavement to create a free surface. The crack results from the high tensile forces or stresses imposed on the unheated material between the spaced heat patterns or zones produced by the microwave energy. The purpose of this free surface is to outline the area within which the pavement is to be fragmented. The fracture or cut therefore should be of sufficient width and depth to terminate fractures formed in the delineated area, as described more fully below. In most cases, a fracture or separation in excess of 0.05 inches width and 4 inches depth is adequate.

Once the free surface delineating the pavement which is to be fragmented is created therein, the pavement within this delineated area is pre-weakened by creating a network of fractures or cracks in it. This preweakening can be accomplished in any one of a number of different ways, however, preferably and advantageously the pre-weakening again is accomplished by use of microwave energy. The pavement fragments bounded by these fractures are tightly interlocked, in view of the fact that the microwave fractures are not flat planes but are undulating surfaces which may pass around rather than out through aggregate particles. As a result of the interlocking, fragment removal is difficult.

Accordingly, in accordance with the method of the invention, to permit these pavement fragments to be more easily removed, a water jet is used to sufficiently pressure the fracture to displace or unkey the pavement fragments on either side of the fracture. This pressurization of the fractures results in propagation of the fracture, unless the fracture terminates at a surface that provides pressure relief. Propagation of the fractures naturally enhances the fragmentation process.

In order to implement the water-jet effect, it is necessary to introduce water into the fractures. If the pulse of water impacts the surface of the pavement at a fracture, water is introduced into the fracture. If it does not, the fractures can be pressurized, by using the water jet to bore a hole into the pavement which intersects the fracture network. Since the microwave fractures are not flat plane surfaces but are curved and undulating, the fracture surface as projected against the pavement surface may be a significant proportion of the total pavement surface area.

Boring a hole in pavement by water jets is accomplished by exceeding the strength of the cement paste and aggregate and continues until a depth is reached where the pressure of the bottom of the hole is less than the strength of the material. The pressure at the base of the hole decreases with depth due to energy dissipation by jet mixing. After penetration ceases, the incoming water in the jet turns back on itself with the water flowing annularly out of the hole like a fountain. The hole is bored within a short time after impact.

Where existing fractures are intersected, the water enters the fractures and initiates the fragmentation mechanisms described above. The water pressure in the cavity must exceed a certain threshold pressure before water can enter the fracture since the fracture represents a resistance to flow. The resistance is a function of both the exposed length of the fracture and its width. Resistance to the entry of water may vary from negligible to a value approaching that required to initiate fracturing of the surrounding material.

If in boring a hole in the pavement a fracture is not intersected, the remaining energy in the jet may either be dissipated in the annular flow with a small percentage going into the erosion of the cavity or into pressurizing the fluid in the hole to a value which exceeds hoop tensile stresses in the material around the hole which exceeds the strength of the material and results in radial fractures. In the latter case, the water pressurizes the radiating crack, both propagating it to the nearest free surface and displacing the fracture surfaces to release the pressure. The location of the hole on the surface of the material governs the orientation of the fractures based on the stress distribution. An idealized orientation can be substantially modified since concrete is not isotropic in physical properties and contains discontinuities which serve to orient cracks and other patterns.

In tests conducted with a device capable of producing water pulses of varying pressure through different nozzle diameters, water jet discharges against 2 foot by 2 foot by 6 inch thick concrete specimens of 6,000 psi compressive strength pre-cracked by microwave heating have shown that water jet discharges of between 30,000 and 50,000 psi pressure through a 2 millimeter diameter nozzle are capable of exploiting the microwave fractures and of producing fragmentation. For the same nozzle diameter, pressures between 80,000 and 100,000 psi are required to pressurize the fluid into the hole and initiate fracturing where microwave fractures are not present in the same size block of concrete. Accordingly, by pre-weakening the pavement or concrete in the above-described fashion, the power requirements for producing lower pressure jets of water are substantially less than the power requirments required for the higher pressure jets of water or those necessary to establish compressive wave pulses in the pavement,

as in the above-mentioned US. Pat. No. 3,614,163. As indicated above, a required pressure to produce fracturing in the pavement is in the neighborhood of 30,000 to 50,000 psi. Furthermore, by pre-weakening the pavement and impacting the pre-weakened fracture network, fragmentation thereof to the extent that the pavement fragments are displaced so that they can be more easily removed, by conventional means such as shoveling, can be accomplished at a far greater rate.

In carrying out the method of the invention, the steps as outlined above must be performed in sequence in order to obtain the desired result, fragmented pavement. However, in many typical pavement breaking operations, such as trenching, the three steps may be going on at the same time. The entire length of the trench need not be delineated before microwave preweakening can be started. Similarly, the microwave preweakened pavement may be fragmented by water impact before the length of the trench has been preweakened.

From the above description, it can be seen that an improved low noise method of fragmenting pavement is provided, one which permits controllability of the area of fragmentation, the size of the fragments produced. The method furthermore has a high efficiency or high rate of fragmentation, in comparison to existing methods, and the pavement is fragmented in a manner such that it can be more easiy removed.

It will thus be seen that the objects set forth above, among those made apparent from the preceding description, are efficiently attained and certain changes may be made in carrying out the above method. Accordingly, it is intended that all matter contained in the above description-shall be interpreted as illustrative and not in a limiting sense.

Now that the invention has been described, what is claimed as new and desired to be secured by Letters Patent is:

l. A low noise method for fragmentation of pavement having an upper and lower surface comprising the steps of: creating a continuous free surface delineating the area of pavement which is to be fragmented; fracturing the pavement within the delineated area to preweaken the pavement with fractures extending substantially from the upper to the lower surface thereof; and impacting the fractured pavement with pulses of water at a pressure within a range of 30,000 to 50,000 psi such that the water enters the fractures and pressurizes at least some of the fractures to displace the pavement fragments on either side of the fractures so as to facilitate their removal, said continuous free surface and the pavement within the delineated area being fractured using microwave energy to produce spaced-apart heating patterns at a temperature such as to create stresses therein at least between the heat patterns that exceed the strength of and thereby cause a fracture to occur in the pavement.

2. The method of claim 1, further including the step of impacting the fractured pavement with pulses of water at a pressure to bore a hole into the pavement which intersects at least one of the fractures, the pulses of water after the fracture is intersected pressurizing the fracture and initiating the displacement of the pavement on either side of the fracture.

3. The method of claim 1 further including the steps of impacting the fractured pavement with pulses of water at a pressure to bore a hole into the pavement, and pressurizing the water in the hole to a value which creates hoop tensile stresses in the pavement around the hole which exceed the strength of and thereby cause radial fractures to occur in the pavement.

4. The method of claim 3, further including the step of pressurizing the radial fractures with pulses of water to propogate the radial fractures to the nearest free surface and to displace the pavement on either side of the radial fractures to displace the pavement fragments. 

1. A low noise method for fragmentation of pavement having an upper and lower surface comprising the steps of: creating a continuous free surface delineating the area of pavement which is to be fragmented; fracturing the pavement within the delineated area to pre-weaken the pavement with fractures extending substantially from the upper to the lower surface thereof; and impacting the fractured pavement with pulses of water at a pressure within a range of 30,000 to 50,000 psi such that the water enters the fractures and pressurizes at least some of the fractures to displace the pavement fragments on either side of the fractures so as to facilitate their removal, said continuous free surface and the pavement within the delineated area being fractured using microwave energy to produce spaced-apart heating patterns at a temperature such as to create stresses therein at least between the heat patterns that exceed the strength of and thereby cause a fracture to occur in the pavement.
 2. The method of claim 1, further including the step of impacting the fractured pavement with pulses of water at a pressure to bore a hole into the pavement which intersects at least one of the fractures, the pulses of water after the fracture is intersected pressurizing the fracture and initiating the displacement of the pavement on either side of the fracture.
 3. The method of claim 1 further including the steps of impacting the fractured pavement with pulses of water at a pressure to bore a hole into the pavement, and pressurizing the water in the hole to a value which creates hoop tensile stresses in the pavement around the hole which exceed the strength of and thereby cause radial fractures to occur in the pavement.
 4. The method of claim 3, further including the step of pressurizing the radial fractures with pulses of water to propogate the radial fractures to the nearest free surface and to displace the pavement on either side of the radial fractures to displace the pavement fragments. 